Organosilicon-containing electrolyte compositions having enhanced electrochemical and thermal stability

ABSTRACT

Described are electrolyte compositions and electrochemical devices containing the electrolyte compositions. The compositions include an organosilicon compound, an imide salt and optionally LiPF 6 . The electrolytes provide improved high-temperature performance and stability and will operate at temperatures as high as 250° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of co-pending application Ser. No. 15/038,690,filed May 23, 2016, which is a Section 371 of PCT/US2015/053699, filedOct. 2, 2015, which claims priority to provisional application SerialNo. 62/058,803, filed Oct. 2, 2014, all of which are incorporatedherein.

BACKGROUND

Liquid electrolytes in Li-ion batteries conventionally comprise alithium salt, usually LiPF₆, in an organic solvent blend of ethylenecarbonate (EC) and one or more co-solvents such as dimethyl carbonate(DMC), diethyl carbonate (DEC), or ethylmethyl carbonate (EMC).Unfortunately, LiPF₆ is unstable in these carbonate solvents above 60°C., as well as at charge voltages above 4.3 volts. Operation of a Li-ionbattery above these temperatures or voltages results in rapiddegradation of electrode materials and battery performance. In addition,current Li-ion electrolyte solvents exhibit flashpoints around 35° C.,and are the major source of the energy released during an extreme Li-ioncell failure. Given these significant limitations, current electrolytesare impeding the development of advanced Li-ion batteries for all uses,including portable products, electric drive vehicles (EDVs), and utilityscale use. A dramatic reduction in battery failure rate is also requiredfor large scale Li-ion batteries to effectively serve applications inEDVs and grid storage.

Thus, there is a long-felt and unmet need for improved electrolytesolutions in energy storage devices such as Li-ion batteries.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a series of traces recording current (mA/cm²) versuspotential E_(we)/V for various organosilicon electrolyte compositions(see text for details). The traces were generated using a 1.5 mm Alworking electrode (“we”) in a conventional 3-electrode arrangement.

FIG. 2A is a cyclic voltammogram trace taken at 30° C. using the3-electrode arrangement of FIG. 1 (1.5 mm Al working electrode), with anelectrolyte composition comprising 1M LiTFSI and EC/EMC; the tracerecords the 10^(th) cycle.

FIG. 2B presents a series of traces recording current (mA/cm²) versuspotential E_(we)/V for various organosilicon electrolyte compositionsversus an Al working electrode (see text for details). The trace wasrecorded at 30° C.

FIG. 3A, FIG. 3B, FIG. 3C, and FIG. 3D are a series of voltammogramstaken at 30° C. comparing the performance of the organosilicon- andimide-containing electrolytes disclosed herein versus the correspondingcarbonate-containing electrolytes. See text for complete details.

FIG. 4A, FIG. 4B, FIG. 4C, and FIG. 4D are a series of voltammogramstaken at 50° C. comparing the performance of the organosilicon- andimide-containing electrolytes disclosed herein versus the correspondingcarbonate-containing electrolytes. See text for complete details.

FIG. 5 is a series of cyclic voltammograms for 1M LiTFSI+EC/EMCelectrolytes and 1M LiTFSI/F1S₃MN electrolytes using a conventional3-electrode cell with a 1.5 mm Al working electrode taken at 50° C.; 10cycles are recorded.

FIG. 6A, FIG. 6B, and FIG. 6C are a series of voltammograms taken at 30°C., using the apparatus described in FIG. 5, comparing the performanceof the organosilicon-, carbonate- and imide-containing electrolytesdisclosed herein versus the corresponding electrolytes containing onlycarbonate additives (i.e., no imide additive). See text for completedetails.

FIG. 7A, FIG. 7B, and 7C are a series of voltammograms taken at 50° C.,using the apparatus described in FIG. 5, comparing the performance ofthe organosilicon-, carbonate- and imide-containing electrolytesdisclosed herein versus the corresponding electrolytes containing onlycarbonate additives (i.e., no imide additive). See text for completedetails.

FIG. 8 depicts the results of differential scanning calorimetry (“DSC”)analysis using delithiated commercial Nickel-Cobalt-Aluminum (“NCA”)cathode material in the presence of various electrolytes. See text forfull details.

FIGS. 9A and 9B are a series depicting the results of DSC analysis usingdelithiated commercial Nickel Manganese Cobalt (“NMC”) cathode material(specifically NMC “532,” that is, LiNi_(1/2)Mn_(3/10)Co_(1/5)O₂) in thepresence of various electrolytes.

FIG. 10 is another DSC analysis comparing 0.1 M LiTFSI in combinationwith OS3 electrolytes and an NMC cathode versus other electrolytecompositions. This trace is significant because it indicates that thecombination of an OS3 and LiTFSI has a synergistic effect in DSC testingwith NMC with LiTFSI concentration at from 0.1M to 1.0M. Thesecompositions remain stable at temperatures well above 250° C.

FIG. 11 is a trace depicting cycling stability at 70° C. withimide-containing OS3 electrolytes versus convention carbonate-containingelectrolytes as measured in coin cells with NMC/graphite electrodes.

FIG. 12 is a trace depicting cycling stability at 70° C. with

(F1S₃MN) electrolyte alone and in combination with 20% EC, using LiTFSIor LiPF₆ as the salt. The measurements were taken in coin cells withlithium iron phosphate/graphite electrodes; 1 C charge/2 C discharge;from 3.8 V to 2.5 V; 300 cycles.

FIG. 13 is a trace depicting cycling stability at 70° C. with

(F1S₃M2) electrolyte alone and in combination with 20% EC, using LiTFSIor LiPF₆ as the salt. The measurements were taken in coin cells withlithium iron phosphate/graphite electrodes; 1C charge/2 C discharge;from 3.8 V to 2.5 V; 300 cycles.

DETAILED DESCRIPTION

Disclosed herein are electrolyte compositions comprising at least oneorganosilicon compound and at least one imide-containing compound,typically an imide salt. These compositions display unexpectedlyincreased thermostability. Many of them will operate at temperaturesabove 70° C., above 100° C., above 150° C., above 200° C., and evenabove 250° C.

Disclosed herein are organosilicon (OS) compounds for use as electrolytesolvents in electrochemical devices, among other uses. In general, OScompounds are environmentally friendly, non-flammable, hightemperature-resistant materials. These characteristics make OS materialswell-suited for use as electrolyte solvents, binders, and coatings inenergy storage devices. OS-based electrolytes are compatible with alllithium (Li) based electrochemical systems, including primary andrechargeable batteries, (i.e. Li-ion, Li-air), and capacitors (i.e.super/ultra-capacitors). The process of designing OS-based electrolytesinto a Li battery involves limited changes in the cell design, and theseelectrolytes can be incorporated into production operations withexisting manufacturing processes and equipment.

The OS-containing electrolytes described herein can be used as liquidelectrolyte solvents that replace the carbonate-based solvent system intraditional Li-ion batteries. The OS-based solvents provide significantimprovements in performance and abuse tolerance in Li-ion batteries,including increased thermal stability for longer life at elevatedtemperatures, increased electrolyte flash points for improved safety,increased voltage stability to allow use of high voltage cathodematerials and achieve higher energy density, reduced battery failurerates for consistency with the requirements for large scale Li batteriesused in electric drive vehicles and grid storage applications, andcompatibility with materials currently in use in Li-ion batteries forease of adoption in current designs. Electrical double-layer capacitor(EDLC) devices have also demonstrated functionality with OS-basedelectrolytes. The OS compounds described herein can be used in OS-basedelectrolyte blends to meet the requirements of specific applications inthe industrial, military, and consumer product devices.

Specifically disclosed herein are:

1. An electrolyte composition comprising, in combination:

an organosilicon compound and an imide salt and optionally LiPF6;

wherein when subjected to cyclic voltammetry at a plurality of cyclesranging from about 3V to about 5V and using a cathode current collectorcomprising aluminum versus Li/Li⁺electrodes the composition exhibits anoxidative corrosion current of about 0.10 mA/cm² or less for a secondand subsequent cycles.

2. The electrolyte composition of claim 1, wherein the organosiliconcompound is selected from the group consisting of Formula I or FormulaII:

wherein R¹ , R², and R³ are the same or different and are independentlyselected from the group consisting of C₁ to C₆ linear or branched alkyland halogen;

“Spacer” is selected from the group consisting of C₁ to C₆ linear orbranched alkylene, alkenylene, or alkynylene, or “Spacer” is absent,provided that when “Spacer” is absent, Y is present;

Y is absent or is selected from the group consisting of—(O—CH₂—CH₂)_(n)— and

wherein each subscript “n” is the same or different and is an integerfrom 1 to 15, and subscript “x” is an integer from 1 to 15; and each R⁴is the same or different and is selected from the group consisting ofcyano (—CN), cyanate (—OCN), isocyanate (—NCO), thiocyanate (—SCN) andisothiocyanate (—NCS).

3. The electrolyte composition of claim 2, wherein the organosiliconcompound has a structure as shown in Formula I.

4. The electrolyte composition of claim 2, wherein the organosiliconcompound has a structure as shown in Formula II.

5. The electrolyte composition of claim 2, wherein imide salt comprisesa bis(trifluoromethane)sulfonamide (TFSI) anion.

6. The electrolyte composition of claim 5, further comprising lithiumbis(oxalato)borate (LiBOB) or LiPF6.

7. The electrolyte composition of claim 6, further comprising acarbonate.

8. The electrolyte composition of claim 7, wherein the carbonate isselected from the group consisting of ethylene carbonate (EC), dimethylcarbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC),propylene carbonate (PC), and fluoroethylene carbonate (FEC).

9. The electrolyte composition of claim 7, comprising LiBOB.

10. The electrolyte composition of claim 1, wherein the organosiliconcompound is selected from the group consisting of Formula I or FormulaII:

wherein R¹ , R², and R³ are the same or different and are independentlyselected from the group consisting of C₁ to C₆ linear or branched alkyland halogen;

“Spacer” is selected from the group consisting of C₁ to C₆ linear orbranched alkylene, alkenylene, or alkynylene, or “Spacer” is absent,provided that when “Spacer” is absent, Y is present;

Y is absent or is selected from the group consisting of—(O—CH₂—CH₂)_(n)— and

wherein each subscript “n” is the same or different and is an integerfrom 1 to 15, and subscript “x” is an integer from 1 to 15; and each R⁴is the same or different and is selected from the group consisting ofcyano (—CN), cyanate (—OCN), isocyanate (—NCO), thiocyanate (—SCN) andisothiocyanate (—NCS);

the imide salt is bis(trifluoromethane)sulfonimide lithium salt(LiTFSI); and

wherein the electrolyte composition further comprises lithiumbis(oxalato)borate (LiBOB) or LiPF₆ and further comprises a carbonate.

11. The electrolyte composition of claim 10, wherein the organosiliconcompound has a structure as shown in Formula I.

12. The electrolyte composition of claim 10, wherein the organosiliconcompound has a structure as shown in Formula II.

13. The electrolyte composition of claim 10, wherein the carbonate isselected from the group consisting of ethylene carbonate (EC), dimethylcarbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC),propylene carbonate (PC), and fluoroethylene carbonate (FEC)

14. The electrolyte composition of claim 13, further comprising LiBOB.

15. The electrolyte composition of claim 1, wherein the compositionexhibits a differential scanning calorimetric (DSC) response onsettemperature that is at least 5° C. higher than a corresponding DSCresponse onset temperature of the organosilicon compound absent theimide salt.

16. The electrolyte composition of claim 15, wherein the organosiliconcompound is selected from the group consisting of Formula I or FormulaII:

wherein R¹ , R², and R³ are the same or different and are independentlyselected from the group consisting of C₁ to C₆ linear or branched alkyland halogen;

“Spacer” is selected from the group consisting of C₁ to C₆ linear orbranched alkylene, alkenylene, or alkynylene, or “Spacer” is absent,provided that when “Spacer” is absent, Y is present;

Y is absent or is selected from the group consisting of—(O—CH₂—CH₂)_(n)— and

wherein each subscript “n” is the same or different and is an integerfrom 1 to 15, and subscript “x” is an integer from 1 to 15; and each R⁴is the same or different and is selected from the group consisting ofcyano (—CN), cyanate (—OCN), isocyanate (—NCO), thiocyanate (—SCN) andisothiocyanate (—NCS).

17. The electrolyte composition of claim 16, wherein the organosiliconcompound has a structure as shown in Formula I.

18. The electrolyte composition of claim 16, wherein the organosiliconcompound has a structure as shown in Formula II.

19. The electrolyte composition of claim 16, wherein imide saltcomprises a bis(trifluoromethane)sulfonamide (TFSI) anion.

20. The electrolyte composition of claim 19, further comprising lithiumbis(oxalato)borate (LiBOB) or LiPF6.

21. The electrolyte composition of claim 20, further comprising acarbonate.

22. The electrolyte composition of claim 21, wherein the carbonate isselected from the group consisting of ethylene carbonate (EC), dimethylcarbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC),propylene carbonate (PC), and fluoroethylene carbonate (FEC).

23. The electrolyte composition of claim 22, comprising LiBOB.

24. An electrochemical device comprising an electrolyte composition asrecited in any one of claims 1 to 23.

The objects and advantages of the compounds and electrolyte formulationswill appear more fully from the following detailed description andaccompanying drawings.

The term “organosilicon compound” and the abbreviation “OS” aresynonymous and designate any organic compound comprising at least onecarbon atom, hydrogen atoms, and at least one silicon atom, and which iscapable of functioning in an electrolytic environment, withoutlimitation. Organosilicon compounds may also additionally (andoptionally) comprise at least one oxygen atom, at least one nitrogenatom, at least one halogen atom, and/or at least one sulfur atom.Explicitly included within the term “organosilicon” are theorganosilicon compounds disclosed in U.S. Pat. Nos: 8,765,295;8,076,032; 8,076,031; 8,027,148; 7,695,860; 7,588,859; 7,473,491, and WO2013/16836 A1 all of which are incorporated herein by reference.

The term “OS3” is used herein to designate any compound having astructure as shown in Formulas I, II, III, VI, and V:

wherein R¹ , R², and R³ are the same or different and are independentlyselected from the group consisting of C₁ to C₆ linear or branched alkyland halogen;

“Spacer” is absent or is selected from the group consisting of C₁ to C₆linear or branched alkylene, alkenylene, or alkynylene, provided thatwhen “Spacer” is absent, Y is present;

Y is absent or is selected from the group consisting of—(O—CH₂—CH₂)_(n)— and

wherein each subscript “n” is the same or different and is an integerfrom 1 to 15, and subscript “x” is an integer from 1 to 15; and each R⁴is the same or different and is selected from the group consisting ofcyano (—CN), cyanate (—OCN), isocyanate (—NCO), thiocyanate (—SCN) andisothiocyanate (—NCS).

Also specifically disclosed herein are compounds of Formula I, wherein“Spacer” is present, and Y is —(O—CH₂—CH₂)_(n)—. Additionally,specifically disclosed herein are compounds in which “Spacer” is presentand Y is

Additionally disclosed herein are compounds in which “Spacer” is absent,and Y is —O—CH₂—CH₂)_(n)—.

Also disclosed herein are compounds having a structure as shown in anyof Formulas III, IV, and V:

wherein R¹, R², and R³ are the same or different and are independentlyselected from the group consisting of C₁ to C₆ linear or branched alkyland halogen; “spacer” is a C₁ to C₆ linear or branched alkylene,alkenylene, or alkynylene; each R⁴ is the same or different and isselected from the group consisting of cyano (—CN), cyanate (—OCN),isocyanate (—NCO), thiocyanate (—SCN) and isothiocyanate (—NCS); eachsubscript “n” is the same or different and is an integer from 1 to 15;“x” is an integer from 1 to 15. Also included herein are electrolytecompositions comprising one or more of the compounds of Formulas Ithrough V as described herein, in combination with a salt, preferably alithium-containing salt.

R¹, R², and R³ may optionally be selected from the group consisting ofC₁ to C₃ alkyl, chloro, and fluoro; and R⁴ may optionally be cyano.

When the compound comprises Formula II, R¹ and R³ may optionally beselected from the group consisting of C₁ to C₃ alkyl (or simply methyl),chloro, and fluoro. Each “n” is optionally and independently an integerfrom 1 to 5. R⁴ may optionally be cyano.

When the compound comprises any of Formulas III through V, R¹, R², andR³ may optionally be selected from the group consisting of C₁ to C₃alkyl, chloro, and fluoro. In some versions of the Formula III-Vcompounds at least one of R¹, R², and R³ is halogen; in other versionsof the Formula III- V compounds at least two of R¹, R², and R³ arehalogen. The “spacer” may optionally be a C₂ to C₄ linear or branchedalkylene. R⁴ may optionally be cyano.

When the compound comprises any of Formulas III through V, R¹, R², andR³ may optionally be selected from the group consisting of C₁ to C₃alkyl, chloro, and fluoro. In some versions of the Formula I-V compoundsat least one of R¹, R², and R³ is halogen; in other versions of theFormula I-V compounds at least two of R¹, R², and R³ are halogen. The“spacer” may optionally be a C₂ to C₄ linear or branched alkylene. R⁴may optionally be cyano. In certain versions of the Formula IIcompounds, “x” may optionally be 1 to 4.

In all versions of the compounds, “halogen,” includes fluoro, chloro,bromo, and iodo. Fluoro and chloro are the preferred halogensubstituents. The term “lithium-containing salt” explicitly includes,but is not limited to, LiClO₄, LiBF₄, LiAsF₆, LiPF₆, LiCF₃SO₃,Li(CF₃SO₂)₂N, Li(CF₃SO₂)₃C, LiN(SO₂C₂F₅)₂, lithium alkylfluorophosphates and lithium bis(chelato)borates.

The term “carbonate” refers to any compound, without limitation, thatincludes at least one CO₃ (i.e., O—C(═O)—O) moiety, including organiccarbonates, cyclic carbonates, etc.

All of the above-disclosed compounds and any individual compound orcombination of such compounds is generically designated herein as “OS”compound(s).

Also disclosed herein are electrolyte compositions comprising one ormore OS compounds as recited in the preceding paragraphs in combinationwith an imide. Also disclosed herein are electrochemical devicescomprising such electrolyte compositions. The compounds disclosed hereinare highly useful for formulating electrolytes for use in charge-storagedevices of all kinds (e.g., cells, batteries, capacitors, and the like).

Throughout the description, a number of shorthand abbreviations will beused to designate various organosilicon compounds more easily. Thefollowing conventions are used:

The nNDnN compounds have the general formula:

wherein R¹ and R³ are the same or different and are independentlyselected from the group consisting of C₁ to C₆ alkyl, each R² is thesame or different and is independently selected from the groupconsisting of cyano (—CN), cyanate (—OCN), isocyanate (—NCO),thiocyanate (—SCN) and isothiocyanate (—NCS), and the two subscripts “n”are integers that are the same or different and independently range from1 to 15. Thus, for example, 1ND1N is the compound wherein R¹ and R³ aremethyl (i.e., C₁) and both subscripts “n” are 1.

The FnS_(n)MN compounds have the general formula:

wherein R¹, R², and R³ are the same or different and are independentlyselected from the group consisting of C₁ to C₆ alkyl (preferably methyl)and halogen (preferably F), “spacer” is a C1 to C6 linear or brancheddivalent hydrocarbon (i.e., alkylene, alkenylene, alkynylene), and R⁴ isselected from the group consisting of cyano (—CN), cyanate (—OCN),isocyanate (—NCO), thiocyanate (—SCN) and isothiocyanate (—NCS). Thecompounds designated SnMN have the same structure, wherein R¹, R², andR³ are the same or different and are independently selected from thegroup consisting of C₁ to C₆ alkyl (preferably methyl).

Related compounds disclosed herein have the structures:

wherein R¹ , R², and R³ are the same or different and are independentlyselected from the group consisting of C₁ to C₆ alkyl (preferably methyl)and halogen (preferably F), “spacer” is a C1 to C6 linear or brancheddivalent hydrocarbon (i.e., alkylene, alkenylene, alkynylene), R⁴ isselected from the group consisting of cyano (—CN), cyanate (—OCN),isocyanate (—NCO), thiocyanate (—SCN) and isothiocyanate (—NCS), and “x”is an integer of from 1 to 15, preferably from 1 to 4.

The compounds disclosed herein can be made by a number of differentroutes. A general approach that can be used to fabricate the compoundsis as follows:

The various R groups are as defined herein; “n” is a positive integer.

The compounds disclosed herein can also be fabricated via the followingapproach:

The compounds disclosed herein are also made by a number of specificroutes, including the following reaction schemes:

An “imide” is defined herein to be a compound comprising two acyl groupsbonded to a nitrogen atom, i.e.:

wherein R¹, R², and R³ are the same or different can be a very widevariety of atoms, including hydrogen, halogen, metals, aliphatic groups(substituted or unsubstituted; linear, branched, or cyclic), aryl groups(substituted or unsubstituted), carbonates, cyclic carbonates, etc. R¹may also be absent, in which case the central nitrogen atom will bear anegative charge and can form salts. “X” is any atom that will support atleast one acyl group, such as carbon (which will support only one acylgroup per carbon atom) or sulfur, which can support two acyl groups persulfur atom (i.e., X and its attendant acyl moieties define a sulfonegroup).

An “imide salt” is any salt containing an “imide” as defined herein. Asused in this context “salt” has its conventional meaning of a chemicalcompound formed from the reaction of an acid with a base. An exemplaryimide salt that can be used in the present electrolyte compositionsinclude Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (i.e.,bis(trifluoromethane)sulfonimide lithium salt, Sigma-Aldrich Catalog No.449504). LiTFSI is a commercial product supplied by severalinternational suppliers:

The TFSI anion forms a great many other imide salts, which areexplicitly included within the scope of the term “imide salt,” includingimide salts that are sometimes referred to as “ionic liquids,” includingthe following:

Tetrabutylammonium bis-trifluoromethanesulfonimidate (Fluka Catalog No.86838):

1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (FlukaCatalog No. 11291)

Diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide(Sigma-Aldrich Catalog No. 727679):

Methyl-trioctylammonium bis(trifluoromethylsulfonyl)imide (Fluka CatalogNo. 00797)

Triethylsulfonium bis(trifluoromethylsulfonyl)imide (Fluka Catalog No.8748)

Additional examples of imide salts that can be used herein are describedin the scientific literature. See, for example, J. Phys. Chem. B 2005,109, 21576-21585, which describes imide salts having the followingstructure:

See also J. Phys. Chem. B 2007, 111, 4819-4829.

Structurally related imide salts are also described in Chem. Commun.,2011, 47, 11969-11971:

Still further imide salts are described in Ionics (2014) 20:1207-1215,and may be used in the compositions disclosed and claimed herein,including:

“LiBOB” refers to lithium bis(oxalato)borate:

The elements and method steps described herein can be used in anycombination whether explicitly described or not.

All combinations of method steps as used herein can be performed in anyorder, unless otherwise specified or clearly implied to the contrary bythe context in which the referenced combination is made.

As used herein, the singular forms “a,” “an,” and “the” include pluralreferents unless the content clearly dictates otherwise.

Numerical ranges as used herein shall include every number and subset ofnumbers contained within that range, whether specifically disclosed ornot. Further, these numerical ranges shall be construed as providingsupport for a claim directed to any number or subset of numbers in thatrange. For example, a disclosure of from 1 to 10 shall be construed assupporting a range of from 2 to 8, from 3 to 7, from 5 to 6, from 1 to9, from 3.6 to 4.6, from 3.5 to 9.9, and so forth.

It is understood that the compounds and compositions disclosed hereinare not confined to the particular construction and arrangement of partsherein illustrated and described, but embraces such modified formsthereof as come within the scope of the claims.

One class of organosilicon compounds that can be used in the disclosedelectrolyte compositions are organosilicon compounds having a sharedstructural feature in the form of one or more terminal substituents thatcomprise a carbon-nitrogen double or triple bond, such as a cyano(R—C≡N), cyanate (R—O—C≡N), isocyanate (R—N═C≡O), thiocyanate (R—S—C≡N),and/or isothiocyanate (R—N═C═S). Included among the preferred compoundsare the following structures:

Of particular note in the present electrolytes is a wholly unexpectedsynergism when OS compounds are formulated with imides compounds ingeneral, lithium-containing imides salts, and LiTFSI in particular, bothin the presence or absence of additional carbonate additives.Electrolyte compositions comprising OS compounds admixed with imidesalts exhibit unexpectedly improved electrochemical and thermalproperties. Thus, disclosed herein are improved electrolytes comprisingan OS compound in combination with an imide.

Referring now to the drawings, it has been found that imide salts, whenblended with OS compounds, yield electrolyte compositions having loweraluminum oxidation potentials as compared to electrolytes consisting ofan OS compound in combination with just carbonate additives. Asdiscussed below, the combination of OS compounds and LiTFSI shows asynergistic effect in DSC testing with NMC with LiTFSI at OSconcentrations from about 0.1M to about 1.0M. (Concentrations above andbelow this range are explicitly within the scope of the attachedclaims.) This result indicates fundamental properties for improved abuseresistance in full cells and other electrochemical devices. Imide saltshave been used in lithium ion batteries in the past. However, their usehas been limited due to pronounced aluminum corrosion andelectrochemical breakdown at higher voltages when used in conjunctionwith carbonate-only electrolytes. The electrolytes described herein,namely, OS compound(s) in combination with imide salts enable imidesalt-containing electrolytes to achieve greatly improved thermal andelectrochemical stability in lithium ion batteries and otherelectrochemical devices.

FIG. 1 illustrates the increased Al oxidation potentials exhibited bythe electrolyte compositions disclosed herein. FIG. 1 presents a seriesof traces recording current (mA/cm²) versus potential E_(we)/V forvarious organosilicon electrolyte compositions. The traces weregenerated using a 1.5 mm Al working electrode (“we”) in a conventional3-electrode arrangement. (All of the cyclic voltammetry data presentedherein was gathered using this same 1.5 mm Al working electrode.) Theelectrolyte compositions tested include OS compounds in combination withcarbonate additives and LiTFSI and LiPF₆. Of particular relevance inFIG. 1 is that the lowest Al corrosion seen among the compositionstested was for 0.25M LiTFSI and OS. Additionally, the OS+LiTFSI hadlower corrosion rates than compositions consisting only of carbonateswith LiTFSI salt, and carbonate blended with LiTFSI+LiPF₆ salts. Thevarious electrolyte compositions tested are summarized in Table 1.1. Theresulting oxidation voltages are presented in Table 1.2. Table 1.3matches the various electrolyte compositions tested to the figures inwhich the results of the testing are presented.

TABLE 1.1 Electrolyte compositions tested. Electrolyte Compositionsolvents salts F1S₃MN EC/EMC (3/7v) 1M LiPF₆ ZP815 EPG2 1M LiTFSI ZT817ET1088 0.25M LiTFSI + 0.75M LiPF₆ ZP1110 EP1129

TABLE 1.2 Oxidation voltage: Oxidation Voltage Electrolyte @ 1 mA/cm²EPG2-03 >8 V ET1088-01 5.0 V EP1129-01 >8 V ZP815-17 >8 V ZT817-02 6.2 VZP1110-01 >8 V

TABLE 1.3 Electrolyte compositions by electrolyte code as used in thefigures electrolyte FIG. code Solvents Salts Additives  1 ET1088 EC/EMC:1M LiTFSI none 30/70 vol % ZT817 100% F1S₃MN 1M LiTFSI none ZP815 100%F1S₃MN 1M LiPF₆ none EPG2 EC/EMC: 1.2M LiPF₆ none 30/70 vol % EP1129EC/EMC: 0.25M LiTFSI + none 30/70 vol % 0.75M LiPF₆ ZP1110 100% F1S₃MN0.25M LiTFSI + none 0.75M LiPF₆  8 (1) EC/EMC: 0.25M LiTFSI + 2% VCEP1094 30/70 vol % 0.75M LiPF₆ (2) EC/EMC: 1M LiPF₆ 2% VC + 0.05M EPG630/70 vol % LiBOB (3) F1S₃MN/EC/DEC: 0.25M LiTFSI + 2% VC + 0.05M ZP11022/2/6 vol % 0.75M LiPF₆ LiBOB (4) F1S₃MN/EC/EMC: 1M LiPF₆ 2% VC + 0.05MZP967 2/2/6 vol % LiBOB (5) F1S₃MN/EMC: 0.25M LiTFSI + 2% VC + 0.05MZP1132 5/5 vol % 0.75M LiPF₆ LiBOB (6) F1S₃MN/EMC: 1M LiPF₆ 2% VC +0.05M ZP937 5/5 vol % LiBOB (7) F1S₃MN/EC: 0.25M LiTFSI + 2% VC + 0.05MZP1131 8/2 vol % 0.75M LiPF₆ LiBOB (8) F1S₃MN/EC: 1M LiPF₆ 2% VC + 0.05MZP826 8/2 vol % LiBOB 12 ZT1534 98% F1S₃MN 1M LiTFSI 2% VC + 0.1M LiDFOBZT1529 F1S₃MN/EC: 1M LiTFSI 2% VC + 0.05M 78/20 vol % LiBOB ZP826F1S₃MN/EC: 1M LiPF₆ 2% VC + 0.05M 78/20 vol % LiBOB ZP1533 98% F1S₃MN 1MLiPF₆ 2% VC + 0.1M LiDFOB 13 XT1532 98% F1S₃M2 1M LiTFSI 2% VC + 0.1MLiDFOB XT1530 F1S₃M2/EC: 1M LiTFSI 2% VC + 0.05M 78/20 vol % LiBOBXP1531 98% F1S₃M2 1M LiPF₆ 2% VC + 0.1M LiDFOB XP490 F1S₃M2/EC: 1M LiPF₆1% VC + 0.05M 79/20 vol % LiBOB  9A EPG2 EC/EMC: 1.2M LiPF₆ none 30/70vol % ET1088 EC/EMC: 1M LiTFSI none 30/70 vol % EP1129 EC/EMC: 0.25MLiTFSI + none 30/70 vol % 0.75M LiPF₆  9B EPG2 EC/EMC: 1.2M LiPF₆ none30/70 vol % ZP815 100% F1S₃MN 1M LiPF₆ none ZP817 100% F1S₃MN 1M LiTFSInone ZP1110 100% F1S₃MN 0.25M LiTFSI + none 0.75M LiPF₆ 11 EP1173EC/EMC/DEC 0.1M LiTFSI + 1M 1% VC, 1% PS (3/3.5/3.5v) LiPF₆ 0.1M LiBOB,0.1M LiDFOB ZP1168 F1S₃MN/EC/EMC/DEC 0.1M LiTFSI + 1M 1% VC, 1% PS(2/2/3/3v) LiPF₆ 0.1M LiBOB, 0.1M LiDFOB

FIG. 2A and 2B illustrate that electrolyte compositions comprising OS3combined with LiTFSI are stable with Al and do not show oxidativepitting corrosion (which is a problem with carbonate/OS electrolytes).FIG. 2A is a cyclic voltammogram trace taken at 30° C. using the3-electrode arrangement of FIG. 1 (1.5 mm Al working electrode), with anelectrolyte composition comprising 1M LiTFSI and EC/EMC; the tracerecords the 10^(th) cycle. FIG. 2B presents a series of traces recordingcurrent (mA/cm²) versus potential E_(we)/V for various organosiliconelectrolyte compositions versus an Al working electrode (see text fordetails). The trace was recorded at 30° C. All measurements were takenwith a 1.5 mm Al working electrode in a conventional 3-electrode cell,on the 10th cycle. FIG. 2A depicts the results for 1M LiTFSI+EC/EMC(3:7v). FIG. 2A depicts the results for:

-   -   1) 1M LiTFSI+F1S₃MN    -   2) 0.25M LiTFSI+0.75M LiPF₆+EC/EMC (3/7v)    -   3) 0.25M LiTFSI+0.75M LiPF₆+F1S₃MN

FIG. 3A, FIG. 3B, FIG. 3C, and FIG. 3D are a series of voltammogramstaken at 30° C. comparing the performance of the organosilicon- andimide-containing electrolytes disclosed herein versus the correspondingcarbonate-containing electrolytes. The 3-electrode cell describedearlier was used to generate the data. This series of graphs clearlyshows that aluminum oxidation is reduced with the OS3/imide solventsystem disclosed herein as compared to carbonate-only/imide systems.FIG. 3A shows the results for 1M LiTFSI+EC/EMC, 3:7v. FIG. 3B shows theresults for 1M LiTFSI+F1S₃MN. FIG. 3C shows the results for 0.25MLiTFSI+0.75M LiPF₆+EC/EMC, 3:7v. FIG. 3D shows the results for 0.25MLiTFSI+0.75M LiPF₆+F1S₃MN.

The series of traces depicted in FIGS. 4A, 4B, 4C, 4D correspond tothose in FIGS. 3A, 3B, 3C, and 3D, but were conducted at 50° C. (ratherthan 30° C.). FIG. 4A shows the results for 1M LiTFSI+EC/EMC, 3:7v. FIG.4B shows the results for 1M LiTFSI+F1S₃MN. FIG. 4C shows the first cycleof 1M LiTFSI+EC/EMC (3:7v) superimposed on top of the correspondingtrace for 1M LiTFSI+F1S₃MN. FIG. 4D depicts the same traces as in FIG.4C at the 10^(th) cycle.

FIG. 5 further illustrates the oxidative stability of Al at 50° C. whenusing the disclosed OS3 and carbonate electrolytes combined with LiTFSI.FIG. 5 clearly shows that OS3 electrolyte shows great advantage overcarbonate in a LiTFSI system, especially at 50° C. The figure showssuperimposed voltammograms for 1M LiTFSI+EC/EMC electrolytes and 1MLiTFSI/F1S₃MN electrolytes using a conventional 3-electrode cell with a1.5 mm Al working electrode taken at 50° C.; 10 cycles are recorded.

FIGS. 6A, 6B, and 6C illustrate the oxidative stability of Al at 30° C.when using the electrolyte composition disclosed herein. In short,reduced aluminum oxidation was also observed when OS3 compounds wereblended with EMC and LiTFSI. The current density during the first cycleincreases with the amount of EMC blended with OS3. After 10 cycles, thecurrent densities decrease to the same level. FIG. 6A is the trace for1M LiTFSI+F1S₃MN. FIG. 6B is the trace for 1M LiTFSI+F1S₃MN/EMC (8/2v).FIG. 6C is the trace for 1M LiTFSI+F1S₃MN/EMC (5/5v).

FIGS. 7A, 7B, and 7C correspond to the results shown in FIGS. 6A, 6B,and 6C, but run at 50° C. FIG. 7A is the trace for 1M LiTFSI+F1S₃MN.FIG. 7B is the trace for 1M LiTFSI+F1S₃MN/EMC (8/2v). FIG. 7C is thetrace for 1M LiTFSI+F1S₃MN/EMC (5/5v). As evidenced by these figures,reduced Al oxidation was also observed when OS is blended with EMC andLiTFSI. As in the results at 30° C., at 50° C., the current densityduring the first cycle increases with the amount of EMC blended withOS3. After 10 cycles, the current densities decrease to the same level.

The electrolyte compositions disclosed herein also display unexpectedimproved thermal stability. The thermal stability of various exemplarycompositions was tested using differential scanning calorimetry (DSC) toevaluate their robustness with respect to elevated temperatures.

FIG. 8, for example, is a DSC thermal safety evaluation. Delithiated NCAcathode material was evaluated in presence of various electrolytecompositions described herein. The combination of OS3 and LiTFSI showedsynergistic improvement in DSC testing with NCA at 0.25M LiTFSIconcentration. The following formulations were tested:

-   EC/EMC (3/7v) electrolytes with 0.25M LiTFSI+0.75M LiPF₆ (1); 1M    LiPF₆ (2);-   OS3/EC/EMC (2/2/6v) electrolytes with 0.25M LiTFSI+0.75M LiPF₆ (3);    1M LiPF₆ (4);-   OS3/EMC (1/1v) electrolytes with 0.25M LiTFSI+0.75M LiPF₆ (5); 1M    LiPF₆ (6); OS3/EC (8/2v) electrolytes with 0.25M LiTFSI+0.75M LiPF₆    (7); 1M LiPF₆ (8).

FIGS. 9A and 9B depict DSC thermal safety modeling using delithiated NMC(532) cathode material in presence of various electrolytes. See thefigure itself for complete details. The combination of OS3 and LiTFSIshow synergistic improvement of thermal stability in DSC testing withNMC with LiTFSI concentration at from about 0.1M to about 1.0M.

FIG. 10 is another DSC analysis comparing 0.1 M LiTFSI in combinationwith OS3 electrolytes and an NMC cathode versus other electrolytecompositions. This trace is significant because it indicates that thecombination of an OS3 and LiTFSI has a synergistic effect in DSC testingwith NMC with LiTFSI concentration at from 0.1M to 1.0M.

Overall, the DSC experiments with OS electrolytes in combination withimides shows enhanced thermal stability in the presence of energeticcharged (de-lithiated) cathodes. Preliminary DSC experiments (data notshown) have been conducted with charged NMC and NCA cathode materials. Asignificant improvement in the exotherm onset temperature was achievedwhen OS-based electrolytes with LiTFSI are compared to carbonatebaseline with LiPF₆, OS3+LiPF₆ and carbonates+LiTFSI.

The DSC data clearly show a distinct synergy between OS solvent-basedelectrolytes and imide salts in general and LiTFSI in particular.Fundamental advantages in DSC testing abuse tolerance can be translatedinto a full cell design safety and abuse advantage. Both 1M LiTFSI and0.25M LiTFSI+0.75M LiPF₆ salt formulations with OS and blendedOS/carbonate solvents demonstrated higher exotherm onset temperaturesthan all other variations. For some formulations there was also a lowertotal heat output Formulating the electrolyte composition with even alimited amount (0.1M) of LiTFSI salt in OS electrolyte has a strongeffect on the reactivity of the system, providing a safety advantageover carbonate electrolytes. See especially FIG. 11, which is a tracedepicting cycling stability at 70° C. with imide-containing OS3electrolytes versus convention carbonate-containing electrolytes asmeasured in coin cells with NMC/graphite electrodes. As shown in FIG.11, electrolytes containing 0.1M LiTFSI have excellent high-temperaturecycling performance.

FIGS. 12 and 13 likewise show that electrolyte compositions comprisingOS3 compounds in combination with an imide such as LiTFSI or a lithiumcompound such as LiPF₆ perform admirably over 300 charge/dischargecycles (3.8 V to 2.5 V) at 70° C. This is markedly and unexpectedlybetter performance at this temperature as compared to conventionalelectrolyte compositions.

What is claimed is:
 1. An electrolyte composition comprising, incombination: an organosilicon compound and an imide salt and optionallyLiPF6; wherein when subjected to cyclic voltammetry at a plurality ofcycles ranging from about 3V to about 5V and using a cathode currentcollector comprising aluminum versus Li/Li+electrodes the compositionexhibits an oxidative corrosion current of about 0.10 mA/cm² or less fora second and subsequent cycles; and wherein the composition exhibits adifferential scanning calorimetric (DSC) response onset temperature thatis at least 5° C. higher than a corresponding DSC response onsettemperature of the organosilicon compound absent the imide salt.
 2. Theelectrolyte composition of claim 1, wherein the organosilicon compoundis selected from the group consisting of Formula I or Formula II:

wherein R¹ , R², and R³ are the same or different and are independentlyselected from the group consisting of C₁ to C₆ linear or branched alkyland halogen; “Spacer” is selected from the group consisting of C₁ to C₆linear or branched alkylene, alkenylene, or alkynylene, or “Spacer” isabsent, provided that when “Spacer” is absent, Y is present; Y is absentor is selected from the group consisting of —(O—CH₂—CH₂)_(n)— and

wherein each subscript “n” is the same or different and is an integerfrom 1 to 15, and subscript “x” is an integer from 1 to 15; and each R⁴is the same or different and is selected from the group consisting ofcyano (—CN), cyanate (—OCN), isocyanate (—NCO), thiocyanate (—SCN) andisothiocyanate (—NCS).
 3. The electrolyte composition of claim 2,wherein the organosilicon compound has a structure as shown in FormulaI.
 4. The electrolyte composition of claim 2, wherein the organosiliconcompound has a structure as shown in Formula II.
 5. The electrolytecomposition of claim 2, wherein imide salt comprises abis(trifluoromethane)sulfonamide (TFSI) anion.
 6. The electrolytecomposition of claim 5, further comprising lithium bis(oxalato)borate(LiBOB) or LiPF6.
 7. The electrolyte composition of claim 6, furthercomprising a carbonate.
 8. The electrolyte composition of claim 7,wherein the carbonate is selected from the group consisting of ethylenecarbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC),ethylmethyl carbonate (EMC), propylene carbonate (PC), andfluoroethylene carbonate (FEC).
 9. The electrolyte composition of claim8, comprising LiBOB.
 10. An electrochemical device comprising anelectrolyte composition as recited in any one of claims 1 to 9.